In the intake system of the internal combustion engine, provided are an air duct constituting an intake channel of the internal combustion engine, a resonater or a side branch which is provided in the intake channel of the internal combustion engine and functions for reducing intake noise, and an air cleaner which collects dusts in the intake channel of the internal combustion engine.
When the internal combustion engine is run and thus air is led into the internal combustion, an intake noise may be caused by the intake system's parts. In order to reduce the intake noise, a technique of enhancing the flexural elasticity modulus of the parts and thickening the thickness of the parts has been adapted conventionally. For example, to use a resin composition which is composed of polypropylene resin and talc as a stiffness reinforcing material blended at about 40% by weight of the composition, and to enhance the thickness of the parts have been adapted as the technique. However, such a technique is obliged to be accompanied with a problem of weight increase in the parts.